CD4+ T cells represent an intriguing checkpoint for therapeutic intervention in immune-mediated diseases. This is because the differentiation and subsequent function of CD4+ T cells can be controlled through: 1) manipulation of the T cell receptor (TCR) signaling, 2) modulation of co-stimulatory or inhibitory molecules, and 3) influencing the cytokine milie u. In this context, the cytokine milieu is important for the orchestration of lineage development steps towards either effector T cell (Teff) or regulatory T cell (Treg) phenotypes. As such, the role of cytokines in the differentiation of CD4+ T cells serves as an excellent example to describe the common difficulties encountered in the therapeutic manipulation of immune cell function in physiopathological conditions. One major challenge is the requirement for targeted and highly localized delivery of cytokines to CD4+ cells and not to other cells, because of the pleiotropic effects of cytokines on certain immune cell populations. Another attribute of cytokines is redundancy, and one more intriguing aspect of the immune response is that the combination of certain cytokines can exert well-defined effects only on selected immune cell populations. For example, the combination of TGF-β and IL-2 during antigenic stimulation results in the differentiation of naïve CD4+ T cells into Tregs. However, the simultaneous signaling by TGF-β and the inflammatory cytokine IL-6 not only suppresses the formation of tolerogenic Tregs, but also induces the development of proinflammatory Th17 cells, which have a key promoting role in the pathogenesis of autoimmune disease such as SLE.
Although Tregs have an unequivocal protective role in autoimmune disease, the possible therapeutic use of cytokines for the induction of Tregs is complicated by the fact that an indiscriminate use in vivo of either TGF-β or IL-2 would not be a viable option. In particular, TGF-β is pro-fibrotic, while IL-2 acts on all T cells (thus expanding concurrently both Tregs and Teff populations). Another technical challenge is that a generalized delivery of TGF-β and IL-2 in vivo could result in synergy or counter-regulation of Tregs outcome if other cytokines are present concomitantly in the local milieu.
Tregs that express the Forkhead box protein transcription factor (Foxp3) are a critical subset of CD4+ T cells that maintain homeostasis during infection and tolerance toward self-epitopes. Mutations in Foxp3 can lead to the wasting multiorgan autoimmune condition, IPEX (immune-dysregulation, poly-endocrinopathy, enteropathy, X-linked) in humans. In many common autoimmune diseases such as multiple sclerosis and type 1 diabetes, Tregs become unable to control pathogenic CD4 and CD8 effector cells because of defects on numbers or function. For this reason, strategies to correct these defects and boost their stability have been garnering attention as potential alternatives to the conventional broadly immunosuppressive agents currently in use.
Foxp3+ Tregs are now classified as one of three subsets. The majority of endogenous Tregs, now called nTregs, originate in the thymus and are called tTregs. Others called pTregs are induced from naïve T cells in the periphery. nTregs characteristically display chromatin demethylation at the Foxp3 locus. Tregs require the cytokines IL-2 and TGF-β for fitness and survival. Tregs similar to pTregs called iTregs can also be induced from naïve CD4+ cells ex-vivo by suboptimal TCR signaling in the presence of IL-2 and TGF-β. iTregs were initially believed to be unstable because chromatin remained methylated at the Foxp3 locus. However, in an inflammatory microenvironment nTregs are also unstable and can convert to an effector phenotype. Importantly, recent studies comparing the stability of mouse and human nTregs and iTregs in an inflammatory microenvironment have revealed that only iTregs remain Foxp3+ and can reverse established disease. These findings are supported by the report that Tregs induced in-vivo can also reverse disease in animal models of multiple sclerosis and autoimmune diabetes. However, the methods used to induce these protective iTregs are probably too toxic for translation into a practical immunotherapy.
Thus it is an objection of the invention to provide compositions and methods of use thereof able to safely provide the growth factors needed for stable Tregs.
It is a further object of the invention to provide compositions and methods of use thereof to generate a functionally robust induce CD4 Treg population in-vivo.